GB2060141A

GB2060141A - Anti-surge valve for hydraulic locking device

Info

Publication number: GB2060141A
Application number: GB8031000A
Authority: GB
Priority date: 1979-10-03
Filing date: 1980-09-25
Publication date: 1981-04-29
Also published as: IT8025096A0; FR2466688A1; CA1142413A; BR8005123A; JPS6318066B2; GB2060141B; FR2466688B1; DE3032266A1; DE3032266C2; AU6099880A; JPS5697681A; IT1133677B; AU538360B2; US4480729A

Description

1 GB 2 060 141 A 1

SPECIFICATION Anti-surge valve for hydraulic locking device

The present invention is in the field of hydraulics, and more specifically relates to hydraulic positioning devices of a locking type, 70 which typically are used to control the tilt of seat backs in aircraft.

The anti-surge valve of the present invention is an improvement for use in hydraulic locking devices such as those described in the specifications of British Patent No. 1,151,399 and of British Patent Application No. 7835870 (Serial No. 2,004,975).

Hydraulic locking devices of this type include a moveable piston which separates two working 80 chambers in a cylinder. The working chambers are normally filled to capacity with a hydraulic fluid, and movement of the piston is made possible by a selectively-enabled flow of fluid through a passage extending through the piston. A pressurized fluid reservoir supplies a small compensation flow into and out of the working chambers to compensate for changes in the total volume of fluid in the chambers due to leakage or thermal expansion.

The compensation flow is enabled only when the 90 piston is near one end of its stroke, and the compensation flow velocity is relatively slow because the reservoir is not highly pressurized.

Normally, one end of the hydraulic locking device is attached to a stationary member, and the 95 other end of the hydraulic locking device is attached to a moveable structure which is to be selectively locked at a chosen position. in a typical application, the moveable structure is an arm connected to the tiltable back of a seat. When the 100 seat back is pushed forward, the hydraulic locking device is extended in length.

Such devices include a control pushbutton connected to a control rod which opens a valve enabling flow through the piston, and no problems 105 are encountered with this mode of operation. However, the embodiments of the hydraulic locking device with which the present invention is concerned further include means for operating in an override mode, wherein, when the seat back is 110 pushed forward, pressure produced in one of the working chambers unseats the spring-loaded ball valve within the piston enabling flow of fluid through the piston even though the control pushbutton has not been actuated.

As the hydraulic locking device is being thus extended in the override mode, the pressure rises substantially and rapidly in the working chamber whose volume is being reduced, because of the viscosity of the fluid and the relatively small cross section of the flow passages through the piston. Near the end of the expansion stroke, a bleed orifice in the piston rod which communicates with the chamber whose volume is being reduced, arrives at the port in the cylinder wall that leads to the pressurized reservoir. The pressure in the reservoir is not as great as the transient pressure in the working chamber. When the bleed orifice becomes aligned with the port in the cylinder wall, the high transient pressure in the bleed orifice drives fluid into the reservoir, displacing the spring-loaded reservoir seal.

Because fluid is displaced into the reservoir, instead of into the chamber whose volume is being increased, the total volume of fluid remaining in the working chambers is no longer equal to the total volume of the space of the working chambers. This results in a vacuum space being formed in the chamber whose volume is being increased. This vacuum space manifests itself as backlash or play of the seat back, i.e., inability of the hydraulic device to hold a definite position, with the result that the seat back can freely be moved within a small interval.

In addition to resulting in sloppy positioning of the seat back, the surge of high-pressure fluid into the reservoir displaces the spring- loaded reservoir seal, causing excessive wear of the seal.

Thus, the need was recognized for some means of preventing the highpressure, high-velocity surge of fluid into the reservoir without interfering with the normal low-velocity compensation flow into and out of the reservoir.

According to the present invention there is provided an anti-surge valve to permit a fluid to flow at low velocity into and out of a port that opens into a chamber defined by a wall and to prevent a high-velocity flow of the fluid from the chamber into the port, said anti-surge valve comprising sealing means positioned within the chamber in juxtaposition with the port and extending parallel to the portions of the wall that surrounds the port; spacer means for maintaining said sealing means spaced from the wall in the absence of fluid flow to provide a space for the fluid to flow through in passing between the port and the chamber, whereby such a flow of fluid causes said sealing means to be urged toward the portions of the wall that surround the port by a force related to the velocity of the flow, said sealing means consisting of an elastic material and being sufficiently stiff that at low flow velocities said sealing means is not drawn toward the wall sufficiently to diminish substantially the space between said sealing means and the wall, but being sufficiently flexible thatat high flow velocities said sealing means is drawn against the portions of the wall that surround the port so as to seal the port to prevent high velocity flow of the fluid from the chamber into the port.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing in which:- Fig. 1 is a fractional cross-sectional view of a hydraulic locking device showing the anti-surge valve of the present invention in the hydraulic locking device; and Fig. 2 is a perspective view of the anti-surge valve member. 125 Turning now to the drawings, Fig. 1 shows a preferred embodiment of the anti-surge valve of the present invention in a typical hydraulic locking device. Hydraulic locking devices of this type, but lacking the anti-surge valve of the present 2 GB 2 060 141 A 2 invention, have been known in the art for some time, and are described in the specifications referred to above, which are incorporated herein by reference. For this reason, the hydraulic locking device will not be described in great detail, but instead only those features pertinent to the present invention will be described.

Typically, the hydraulic locking device, as shown in Fig. 1, includes an outer cylinder 12 within which a piston 14 is mounted for axial motion. The 75 piston 14 separates the space within the outer cylinder 12 into two working chambers 16,18, which are sealed at their outer ends by the glands 20, 22, respectively. The working chambers 16, 18 are normally completely filled with hydraulic fluid, and movement of the piston 14 is enabled by a flow of fluid through the piston 14 by way of the passages 24,26, and 28. Taken together, the passages 24, 26, 28 interconnect the chambers 16, 18, but this interconnection is realised only when the ball valve 30 is unseated. In a normal mode, unseating of the ball valve 30 is accomplished by the operator's moving the control rod 32 to the right in Fig. 1. In the override mode, the ball valve 30 is unseated when a high 90 pressure in the working chamber 16 is applied to the left side of the ball valve 30 as viewed in Fig. 1.

As discussed above, the problem with which the present invention is concerned arises in the override mode. When the seat back is pushed forward in the override mode, i.e. without actuating the control rod 32, the piston 14 is pulled to the left as viewed in Fig. 1, tending to decrease the volume of the working chamber 16 and to increase the volume of the working chamber 18. Movement of the piston 14 is facilitated by the flow of hydraulic fluid from the working chamber 16 through the passages 24, 26, 28 into the working chamber 18. Because these passages are relatively small, and in view of the viscosity of the hydraulic fluid, a high- pressure surge is produced in the working chamber 16 when the seat back is pushed forward, particularly if the motion is rather rapid. The high-pressure surge in the working chamber 16 would not in itself be harmful, and the problem arises only because of the way in which the high-pressure surge affects the mechanism included in the hydraulic locking device by means of which the total volume of hydraulic fluid in the working chambers 16, 18 is compensated, by the addition or withdrawal of hydraulic fluid, for volumetric changes caused by temperature fluctuations and leakage.

The fluid compensation system of the hydraulic locking device includes the reservoir 34 which is pressurised by a spring-loaded piston 36, by the slipper seal 38, by the bleed orifice 40 which opens into the cylindrical chamber 42 at the port 44 and by the passage 24. This system is described in the patents referred to above, and an extensive discussion will not be given here. The fluid compensation system is acutated only when the piston 14 has been drawn to its extreme 130 leftward position as viewed in Fig. 1. At this position, the bleed orifice 40 is juxtaposed with the slipper seal 38 and is thereby placed in communication with the pressurised reservoir 34.

Fluid from the reservoir 34 may then flow into the working chambers for replenishment purposes through the bleed orifice 40, into the cylindrical chamber 42, through the passage 24 and the passages 26, 28 into the working chambers 16, 18. It is also possible, with the piston in its extreme leftward position, for excess fluid in the working chambers 16, 18 to be bled back into the reservoir 34 to relieve thermal expansion.

The next three paragraphs describe in detail the problem which the present invention solves. It will be understood that the anti-surge valve member is to be regarded as absent from Fig. 1 for purposes of describing the problem that is solved by installing it.

When the seat back was pushed forward rapidly to its extreme position, thereby creating a pressure surge in the working chamber 16, as the piston neared the leftward end of its stroke, the high pressure in the working chamber 16 was transmitted through the cylindrical chamber 32 and the bleed orifice 40 to cause fluid to surge into the reservoir 34. This surge of fluid into the reservoir reduced the total volume of fluid in the working chambers 16, 18, and specifically resulted in the formation of a vacuum void space in the working chamber 18. As the piston 14 remained in its most leftward position, the pressure in the reservoir 34 and in the highpressure working chamber 16 reached equilibrium, but the equilibrium pressure was not sufficiently great to open the ball valve 30 to permit replenishment of the working chamber 18 from the reservoir 34, and so the void remained in the working chamber 18, and this permitted free travel of the piston to the right, which manifested itself as---play-or - backlashin the positioning of the seat back at all future times. It was found, however, that if the control rod 32 were actuated as or after the seat back was pushed forward, the void in the working chamber 18 was relieved by the normal compensation flow from the reservoir 34. More often than not, aircraft crews did not actuate the control rod 32 because it was not convenient to do so.

Thus, the problem was to find some way of preventing the high pressure surge from the cylindrical chamber 42 from flowing through the port 44 into the bleed orifice passage 40 and thereby into the reservoir 34, without interfering with the normal operation of the fluid compensation system of the locking device in which a low-pressure compensation flow of fluid into and out of the chamber 42 to the port 44 is a normal and essential occurrence.

The-inventor was generally aware that anti surge valves had been built, but these were understood to be large and complex units consisting of many parts and intended for use in industrial pipelines. Such units would be a hundred times the size of the anti-surge valve of 3 GB 2 060 141 A 3 the present invention, wherein the diameter of the cylindrical chamber 42 is typically 0. 168 inches, and were therefore deemed irrelevant to the solution of the present problem. Further, it appeared to be necessary to install the anti-surge valve in the cylindrical chamber 42 of the hydraulic locking device, which is traversed by the axially-extending control rod 32. This unusualshaped available space, as well as the desirability of using as few parts as possible in the anti-surge valve further compounded the problem. It was by no means clear that a simple anti-surge valve could be conceived which would fit into the space between the control rod 32 and the concave wall 46 of the cylindrical chamber 42.

At length, it was found that the anti-surge valve member 10 shown installed in the hydraulic locking device in Fig. 1 and shown in perspective view in Fig. 2, would solve the above-described problem. As can be seen from the drawings, the anti-surge valve member 10 is a unitary structure molded of a resilient elastomeric substance such as buna N rubber in a preferred embodiment, and therefore the anti-surge valve member 10 is both simple and inexpensive.

In the preferred embodiment of the anti-surge valve shown in the Figs. 1 and 2, the anti-surge valve member 10 includes a sealing tube 50 of cylindrical form whose outer diameter is slightly less than the inside diameter of the cylindrical chamber 42. The anti- surge valve member 10 is maintained in coaxial alignment with the cylindrical chamber 42 by means of the flanges 52, 54, located at the ends of the sealing tube 50.

The flanges 52, 54 are sized to extend radially from the outer cylindrical surface of the sealing tube 50 to the inner wall 46 of the cylindrical chamber 42. The flange 52 is provided with a groove 56 which extends in the axial direction from one end to the other of the flange 52. Movement of the anti-surge valve member axially leftward, as viewed in Fig. 1, is prevented by the provision of the end flange 58.

As mentioned above, in the preferred embodiment, the entire anti-surge valve member 10 is a unitary structure consisting of an elastomeric material. In other embodiments, the anti- surge valve member 10 may be an assembly in which the flanges 52, 54 are collars which are affixed at the ends of the sealing tube 50; in this alternative embodiment, the collars are composed of a material different from that used for the sealing tube. For example, in the alternative embodiment, the flanges may be metal.

The operation of the fluid compensation system 120 of the hydraulic locking device remains unaffected by the installation of the anti-surge valve member into the hydraulic locking device in the manner shown in Fig. 1. For purposes of illustration, it will be assumed that the compensation flow is out of 125 the reservoir to replace hydraulic fluid lost by leakage from the system; it is understood that the direction of flow would be reversed if there was a surplus of fluid in the chambers, to transfer the surplus fluid back into the reservoir. Loss of fluid 130 from the working chambers will result in a reduction of pressure in whichever chamber has lost the fluid, and therefore the higher pressure maintained in the reservoir 34 will cause the fipw of fluid from the reservoir to the chamber where the loss of fluid occurred. It will be recalled that the compensation flow is enabled only when the piston is extended fully to the left as viewed in Fig. 1 so that the bleed orifice 40 is brought into communication with the reservoir 34 through the slipper seal 38. The fluid thus flows in sequence from the reservoir 34, through the slipper seal 38, into and through the bleed orifice 40 through the port 44 in the wall 46 of the cylindrical chamber 42 and into the space 60 between the outer surface of the sealing tube 50 and the wall 46 of the cylindrical chamber 42. From thence the fluid flows axially through the groove 56, around the left end of the valve, and into the space 62 between the control rod 32 and the inside wall of the sealing tube 50. The space 62 leads into the passage 24, which in turn opens into the passage 26 and the working chamber 16, and when the ball valve 30 is unseated, into the passage 28 to the working chamber 18. This compensation flow occurs at relatively low velocities because the quantity of fluid is relatively low and the pressure differences therefore are also low.

It is well known from the theory of fluid dynamics that the flow of a fluid over a surface affects the pressure exerted by the fluid on the surface, and the magnitude of the effect generally increases as the velocity increases. For this reason, the pressure on the portion of the outside wall of the sealing tube 50 opposite the port 44 is less than the pressure in the passage 62, since the velocity of the fluid is less in the passage 62. For this reason, even at very low velocities, a force is exerted on the sealing tube urging it toward the port 44. However, because of the relatively low velocity of the compensation flow, the force is extremely weak, and accordingly, the sealing tube 50 is not drawn toward the concave wall 46 sufficiently to diminish substantially the space between the cylindrical outer surface of the sealing tube 50 and the portions of the wall 46 that surround the port 44. Thus, the installation of the anti-surge valve member 10 into the hydraulic locking device does not interfere appreciably with the compensation flow. However, a different situation prevails when the seat back is pushed forward rapidly in the override mode of operation of the hydraulic device.

In that case, a high fluid pressure is produced in the working chamber 16, and this pressure is transmitted at the speed of sound through the passage 26, the passages 24 and 62, and into the cylindrical chamber 42, through the groove 56, and into the space 60 causing the fluid in the space 60 immediately to surge into the port 44 and through the bleed orifice 40 to the reservoir 34. The high pressure causes a high velocity flow of the fluid, particularly in the space 60 surrounding the port 44. According, a much larger force is produced than in the case of the 4 compensation flow, urging the sealing tube 50 toward the port 44. The sealing tube 50 is sufficiently flexible that for the high velocity flow, the cylindrical outer surface of the sealing tube 50 is drawn against the portions of the concave wall 46 that surrounds the port 44 thereby sealing the port almost immediately, and preventing further flow into the port 44.

Those skilled in the art will recognize that the 10. crucial design problem is to assure that the sealing tube is neither too flexible nor too stiff. In the preferred embodiment and best mode, the inside diameter of the cylindrical chamber 42 is 0.168 inches and the outside diameter of the sealing tube 50 is 0. 150 inches in diameter, and the length of the sealing tube between the flanges 52, 54 is 0.312 inches. In this best mode, the anti surge valve is a unitary structure consisting of buna N rubber.

The anti-surge valve of the present invention solves a longstanding problem in the art in a uniquely simple and efficient manner.

Claims

1. An anti-surge valve to permit a fluid to flow at low velocity into and out of a port that opens into a chamber defined by a wall and to prevent a high-velocity flow of the fluid from the chamber into the port, said anti-surge valve comprising sealing means positioned within the chamber in juxtaposition with the port and extending parallel to the portions of the wall that surrounds the port; 80 spacer means for maintaining said sealing means spaced from the wall in the absence of fluid flow to provide a space for the fluid to flow through in passing between the port and the chamber, whereby such a flow of fluid causes said sealing 85 means to be urged toward the portions of the wall that surround the port by a force related to the velocity of the flow; said sealing means consisting of an elastic material and being sufficiently stiff that at low flow velocities said sealing means is 90 not drawn toward the wall sufficiently to diminish substantially the space between said sealing means and the wall, but being sufficiently flexible that at high flow velocities said sealing means is drawn against the portions of the wall that surround the port so as to seal the port to prevent high-veiocity flow of the fluid from the chamber GB

2 060 141 A 4 into the port. 50 2. An anti-surge valve according to claim 1, wherein the chamber is cylindrical and the port is located on the concave wall that defines the cylindrical chamber.

3. An anti-surge valve according to claim 2, wherein the spacer means is a flange surrounding said sealing tube and of sufficient radial thickness to extend radially from the cylindrical outer surface of said sealing tube to the concave wall of the cylindrical chamber.

4. An anti-surge valve according to claim 3, wherein said flange further comprises portions defining a groove that extends axially from one end to the other end of said flange in its outer cylindrical surface.

5. An anti-surge valve according to claim 3 or 4, wherein said flange is located at one end of the cylindrical surface of said sealing means.

6. An anti-surge valve according to any one of claims 2 to 5, wherein said sealing means and said spacer means are parts of a unitary structure.

7. An anti-surge valve according to claim 6, wherein said anti-surge valve is a unitary structure consisting of an elastomeric material.

8. In a hydraulic locking device of the type wherein changes in the total volume of fluid in the working chambers is made up by a low-velocity compensation flow of fluid between a pressurized fluid reservoir and the working chambers, wherein the compensation flow passes through a port that opens into a chamber defined by a wall and communicating with the working chambers, and wherein it is desired to prevent transient highpressure surges in the working chqmbers from driving fluid from the working chambers into the fluid reservoir while not interfering with the relatively gradual compensation flow, an antisurge valve according to any preceding claim.

9. An anti-surge valve to permit a fluid to flow at low velocity into and out of a port that opens into a chamber defined by a wall and to prevent a high-velocity flow of the fluid from the chamber into the port, substantially as hereinbefore described with reference to the accompanying drawing.

10. A hydraulic locking device substantially as hereinbefore described with reference to the accompanying drawing.

Printed for Her Majety's Stationery office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

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